Because of continuing increases in the capacity of a semiconductor memory or in the speed or integration density of a CPU processor, further advancements of microprocesses based on optical lithography are indispensable.
Generally, the limit of microprocesses using optical lithography apparatuses is on an order of the wavelength of light used. For this reason, the wavelengths of light used in optical lithographic apparatuses have been shortened. Currently, near-ultraviolet ray lasers are used, and the microprocessing on a 0.1 micron order is enabled.
Although the minuteness attainable with the optical lithography has advanced, in order to accomplish microprocessing on an order of 0.1 micron or narrower, there still remain many problems to be solved, such as the necessity of shortening the laser wavelength further, or developing lenses usable with such a wavelength region.
On the other hand, as a measure for enabling optical microprocessing on an order of 0.1 micron or narrower, a microprocessing apparatus using a structure of a near-field optical microscope, hereinafter, “SNOM” (Scanning Near-field Optical Microscope), has been proposed. An example is an apparatus in which, by use of evanescent light seeping or escaping from small openings of a size not greater than 100 nm, local exposure exceeding the limit of the wavelength of light is carried out to a resist.
However, in lithographic apparatuses using such an SNOM structure, the microprocessing is carried out on the basis of continuous drawing using one probe (or a few probes). Thus, there is a problem of low throughput.
As a measure for solving this problem, U.S. Pat. No. 6,171,730 discloses a method in which a photomask is formed with a pattern designed so that near-field light seeps from between light blocking films, and the exposure is carried out while the photomask is closely contacted to a photoresist applied to a substrate, so that a fine pattern of the photomask is transferred to the resist at once.
The method and apparatus disclosed in the specification of this patent is excellent, and it makes a large contribution to the technical field to which the present invention belongs.
The near-field exposure method can produce a fine pattern on an order of tens of nanometers, being much smaller than the wavelength of light used for the exposure. For this reason, in the aforementioned U.S. patent, the photomask is provided with a membrane portion and, by flexing it, the membrane portion is approximated to a photoresist up to the near-field region, such that the exposure is carried out in an intimate contact state.
Here, if the alignment operation is carried out while the membrane portion of the photomask and the photoresist are spaced from each other, and if they are subsequently approximated to each other up to the near-field region, and the exposure is carried out in such a state, it may cause a positional deviation of the near-field exposure pattern, due to the flexure of the membrane portion. Also, such a positional deviation may cause a decrease in the yield of the device production.
However, conventional reduction projection system optical lithography or alignment methods for X-ray exposure, using a mask having a membrane portion, are basically an exposure method in which, during the exposure process, the photoresist and the photomask are exposed, while they are kept separated from each other. Thus, in these methods, there is no suggestion for a problem in a case in which, during the exposure process, a photomask and a photoresist are exposed, while they are placed close to or in intimate contact with each other. Therefore, these conventional methods cannot be directly applied to an alignment method for the near-field exposure.
On the other hand, U.S. Pat. No. 6,252,649 discloses an aligner comprising an aligner device for relatively moving and aligning a mask having a pattern depicted thereon to be exposed and an object having a photosensitive layer to be subjected to the exposure through the mask, a contacting device for contacting the mask and the object as aligned, a detecting device for detecting the alignment accuracy of the mask and the object as contacted, separating means responsive to the detecting device for separating the mask and the object from each other when the alignment accuracy of the contacted mask and object is detected by the detecting device, to be out of a predetermined tolerance and in order to align the mask and the object again, and an exposure apparatus for exposing the mask to the object as contacted with each other.
Additionally, the aforementioned U.S. Pat. No. 6,252,649 shows a specific aligner in which a pressure film is used to press a film-mask, thereby to cause deformation of the film-mask. The pressure film is expanded to press the film-mask against the work to closely contact the former to the latter.
However, in the aligner apparatus disclosed in U.S. Pat. No. 6,252,649, the pressure film and the film-mask are made separate, such that there is a space between the pressure film and the film-mask. Thus, if a foreign particle, such as dust, is present in such a space, it may cause incomplete contact of the mask to the workpiece. Even if the close contact is complete, the light projected from a light source would be influenced by the foreign particle, and accurate exposure would be prevented thereby.